In clearing forest, clearing tools have previously been used which normally are mounted on a comparatively long, parallelly guided beam or jib mounted on a forest machine and swingable about its supporting point on the machine. Furthermore, the beam can be moved outwardly from and inwardly towards the machine, in doing which the clearing tool at the end of the beam is maintained on a constant level thanks to the parallel guidance of the beam. The constant level can usually be adjusted. As clearing tool a disc has been used, rotatably driven by a motor, pivotally secured knives or beaters being provided on the periphery of said disc. The knives or beaters will reach a comparatively high speed on account of the large diameter and high rotational speed of the disc, usually about 1500 revolutions per minute (RPM). Moreover, as the knives or beating tools have to be comparatively heavy in order to operate in the desired manner their total kinetic energy will be high. If the beaters strike objects as rocks and pieces of woods these could therefore be thrown far away from the assembly at a high speed, as it is almost impossible to mount a completely covering guard around the rotating disc because, if so, the beaters would not get in touch with the vegetation to be cleared. This device thus requires a very great safety distance, up to 100 m. As the machine itself is of course situated within the safety distance the assembly must also be provided with a guard on the side facing the operator, which means that the assembly only can clear when it is moved outwardly from the machine, or laterally, which is a great disadvantage. A further disadvantage is the fact that it is hard to raise the RPM and thus the capacity of the assembly, as the beaters or knives can then be exposed to such large forces that they may be torn loose. Hence, this previously used device is thus impaired by certain defects.
In an attempt to provide an assembly which is not defective in this way it has been proposed to use a rotating cutter having saw teeth instead of a rotating disc provided with beaters or knives. Such a structure will eliminate in practice the risk of objects being through out from the assembly, which brings with it that the safety distance can be reduced to more normal values. However, the cutter must be protected against contact with larger rocks and the like, as the cutter, in contrast to the pivotally mounted beaters or knives, does not yield upon contact with solid objects. Thus one object of the invention is to provide a guard for the cutter.
Some solutions of this problem can be found in, for example, U.S. Pat. Nos. 4,736,573, 2,532,982 and FR-A-1 548 806, according to which the cutter is protected by means of fixed arms extending radially from the center of the cutter. These known devices are intended, however, for lawn-mowing, hedge trimming etc. and the set of problems and technical solutions which form the basis of these previously known devices cannot quite simply be applied to assemblies for clearing forest, as the properties of the types of vegetation concerned are essentially unlike, primarily with respect to size and resiliency, which makes the demands upon the design of the equipment significantly different.
Moreover, in certain cases, above all when large cutters are concerned which rotate at a comparatively high RPM and/or cutters having a few, large, heavy teeth, it can also be desirable to prevent that objects, e.g. parts coming loose from the cutter, are thrown out from the clearing assembly.
A further object of the invention is thus to provide protective means against objects being thrown out from the clearing assembly.